Direct drive rotor with metal coupler

ABSTRACT

An overmolded-type rotor for an outer rotor-type electric motor, wherein, in addition to a backing ring and magnets, a metallic coupler that comprises an inner axial surface configured to interface with a shaft to be driven by the rotor and an outer axial surface that corresponds to a multiplicity of outer teeth is overmolded with a polymer frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. ProvisionalApplication No. 61/374,578, filed Aug. 17, 2010, which is incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

The present invention is generally directed toward the filed of electricmotors. More specifically, the present invention is directed to outerrotor-type electric motors. Still more specifically, the presentinvention is directed to rotors of outer rotor-type motors, which tendto be useful for use in direct drive clothes washing machines.

BACKGROUND

Direct drive clothes washing machine motor rotors are directly coupledto the shaft that drives the washing machine to transmit the torqueproduced by the motor. The types of rotors used in these applicationsuntil now fall within in two general categories: plastic rotors andsteel rotors. Each general type is associated with advantages anddisadvantages. For example, steel rotors, although relatively strong anddurable, tend to be relatively heavy and costly. In contrast, plasticrotors tend to be lighter and less costly than steel rotors but becausethe plastic typically used is significantly less strong/durable thanmetal, such rotors must be designed to overcome this factor. Typically,the coupling geometry of a plastic rotor must be adjusted to provide arelatively large area of engagement with the drive shaft. This resultsin a plastic rotor typically having a relatively long axial length,which is not desirable especially for horizontal axis washing machines.Relatively, long axial lengths are not limited to plastic rotors,however, many, if not all, steel rotor designs tend to have relativelyoverall long axial lengths.

In view of the foregoing, a need still exists for a rotor having one ormore of the following characteristics: relatively low cost, relativelyshort in axial length, relatively light weight, relativelystrong/durable coupling with the drive shaft.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a rotor for an outer rotor-typeelectric motor, the rotor comprising a metallic coupler that comprises:an inner axial surface configured to interface with a shaft to be drivenby the rotor when the motor is energized; and an outer axial surfacethat corresponds to a multiplicity of outer teeth. The rotor furthercomprising a polymeric frame that comprises a hub molded over at leastthe outer axial surface of the metal coupler; a base that is integrallyformed with the hub and extending radially outward therefrom; a sidewall that is integrally formed with the base; and a multiplicity ofmagnet spacers each of which is integrally formed with the side wall.The rotor further comprising a backing ring of a magnetic materialmolded over by the polymeric frame and having an outer axial surface incontact with the sidewall of the polymeric frame. The rotor stillfurther comprising a multiplicity of permanent magnets in contact withan inner axial surface of the backing ring and molded over by thepolymeric frame and spaced apart by the magnet spacers of the polymericframe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective drawing of a metal coupler of the presentinvention.

FIG. 2 is a perspective cross-section drawing of a rotor of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned above, the present invention is directed to a rotor for anouter rotor-type electric motor. FIGS. 1 and 2 show various aspects,which will be described in greater detail below, of an exemplaryembodiment of the present invention that is useful as part of anelectric motor for operating a clothes washing machine. To be clear, thedirections as set forth herein are in reference to a central axis thatwould be coaxial with the axis of a shaft to which the rotor isconnected as part of an electric motor. Additionally, disclosures oftypical dimensions are in reference to embodiments in which the presentinvention is part of a motor used to operate clothes washing machines.The present invention, however, is applicable to other end uses andadjustments to the various dimensions would be made as appropriate for aparticular end use.

Referring to FIG. 2, the rotor 29 has a height, H_(rotor), whichcorresponds to the greatest distance, measured axially, between any twopoints of the rotor, and an outer diameter, OD_(rotor), whichcorresponds to the greatest distance, measured radially, between any twopoints of the rotor. Typically, H_(rotor) is within the range of about180 mm to about 330 mm (about 7 to about 13 inches) and OD_(rotor) iswithin the range of about 50 mm to about 100 mm (about 2 to about 4inches). For example, in the embodiment depicted in FIG. 2, H_(rotor) isabout 65.5 mm (about 2.58 in) and OD_(rotor) is about 290 mm (about11.38 inches).

Metallic Coupler

Referring to FIGS. 1 and 2, the rotor 29 of the present inventioncomprises, among other things, a metallic coupler 10 having a height,H_(coupler), which corresponds to the greatest distance, measuredaxially, between any two points of the coupler, and a nominal outerdiameter, OD_(coupler), which corresponds to the greatest distance,measured radially, between any two points of the coupler. Typically,H_(coupler) is within the range of about 20 to about 40 mm (about 0.75to about 1.5 inches) and OD_(coupler) is within the range of about 25 toabout 50 mm (about 1 to about 2 inches). For example, in the embodimentdepicted in FIG. 1, H_(coupler) is about 28 mm (about 1.10 in) andOD_(coupler) is about 41.5 mm (about 1.63 in). The metallic coupler 10comprises an inner axial surface 11 configured to interface with a shaftto be driven by the rotor when the motor is energized. The configurationof the inner axial surface may be of nearly any configurationappropriate for the application (e.g., the interface between the inneraxial surface and the shaft to be driven is sufficiently secure androbust to withstand and transmit the torque produced by the motor duringits useful lifetime, which may be simulated by subjecting a rotor to7,500 hours at an average elevated wash torque of 25 N-m with a dutycycle of 13 seconds on and 3 seconds off). For example, the shaft mayhave a circular, square, hexagonal, octagonal, or toothed cross-section(i.e., one or more teeth, which may be, for example, splines, knurl,keys, or combinations thereof) and the inner axial surface will besufficiently complimentary thereto. To be clear, a generally triangulartooth that has a knurled surface has straight sides whereas a generallytriangular tooth that a splined surface has sides that are a curved. Asdepicted in FIG. 1, in one embodiment of the present invention, theinner axial surface 11 comprises a multiplicity of teeth 12, which aresplines.

The metallic coupler 10 further comprises an outer axial surface 13 thatcorresponds to a multiplicity of outer teeth 14. The outer teeth 14 maybe of any configuration (e.g., number, size (e.g., axial length andradial height), shape (e.g., cross-section), spacing (e.g.,circumferential)) that is appropriate for the particular application.More particularly, the foregoing configuration options may be selectedin various combinations such that interface between the outer axialsurface and a polymeric frame (described in greater detail below) issufficiently secure and robust to withstand and transmit the torqueproduce by the motor during its useful lifetime. The outer teeth, forexample, may be selected from the group consisting of knurls, splines,keys, diamond knurls, or combinations thereof. In one embodiment thereare a multiplicity of outer teeth. For example, the number of outerteeth may be at least 10. In another embodiment, the number of outerteeth is least 20 and no more than about 40. In the embodiment depictedin FIG. 1, the outer axial surface 13 comprises a multiplicity of teeth,in particular 30, that are generally triangular with straight sides,which may be referred to as knurls.

The metallic coupler 10 may further comprise one or more annularshoulders 15 radially inward of, and axially outward of each axial endof the outer axial surface 13 and wherein a hub 21 (see below for more adetailed description) is additionally molded over at least one of saidannular shoulders 15 such that it is generally flush with axiallyoutermost exterior surfaces 16 of the metallic coupler.

Polymeric Frame

The rotor of the present invention further comprises a polymeric frame20 that comprises a hub 21 molded over at least the outer axial surfaceof the metal coupler 13. The hub has an outer diameter, OD_(hub), thatis essentially the same as the nominal outer diameter of the couple,OD_(coupler). The polymeric frame further comprises a base 22 that isintegrally formed with the hub 21 and extending radially outwardtherefrom. The base has a thickness, T_(base), which corresponds to thegreatest distance, measured axially, between any two points on theopposite sides of the base. The polymeric frames further comprise a sidewall 23 that is integrally formed with the base 22, wherein the sidewallhas a thickness, T_(sidewall). Typically, T_(base) is within the rangeof about 1.3 to about 3.5 mm (about 0.05 to about 0.14 in). For theembodiment depicted in FIG. 2, T_(base) is about 2.5 mm (about 0.10 in).The polymeric frame also comprises a multiplicity of magnet spacers 24each of which is integrally formed with the side wall 23. The polymericframe may be formed from any polymer appropriate for the application.That said, it is typically desirable to use the lowest cost materialthat has sufficient physical characteristics. For example, the polymericframe may be formed from a filled or non-filled polymer, wherein thepolymer is linear, branched, or crosslinked, and is selected from thegroup consisting of polyester, polyethylene, polypropylene, polyamide,and copolymers thereof. In one embodiment of the present invention thepolymer is polypropylene.

The base 22 of the polymeric frame 20 may comprise a one or moreopenings 25, which may provide benefits such as reduced weight andenhanced cooling. In one embodiment of the present invention thepolymeric frame further comprises a multiplicity of openings 25. Morespecifically, the openings have a total surface area that is within arange that is from about 10% to about 30% of the nominal surface area ofthe base. More typically, the openings have a total surface area that iswithin a range that is from about 10% to about 20% of the nominalsurface area of the base. For example, the embodiment depicted in FIG. 2has a base with a nominal surface area of about 54,220 mm² (about 84in²) and the openings constitute about 8,880 mm² (about 13.75 in²),which is about 16% of the nominal surface area.

Reinforcement Ribs

The polymeric frame may comprise a multiplicity of reinforcement ribs26, 27, 28 each of which integrally formed with at least the base. Inthe depicted embodiment of the present invention each reinforcement ribhas a thickness, T_(rib), that is about equal to T_(base).

Spacer Ribs

One or more of said reinforcement ribs may be integrally formed with amagnets spacer and extend therefrom 26. These ribs may also extend tothe hub and be integrally formed therewith. In the depicted embodimentthe number of these “spacer ribs” corresponds to the number of magnetspacers

Concentric Ribs

One or more of said reinforcement ribs may be concentric with the hub27. Further one or more reinforcement ribs 28 may extend from and beintegrally formed with one or more of said concentric ribs.

Backing Ring

The rotor of the present invention further comprises a backing ring 30having a thickness, T_(br), and a height, H_(br), of a magnetic materialmolded over by the polymeric frame 20 and having an outer axial surface31 in contact with the sidewall 23 of the polymeric frame 20. Typically,T_(br) is within the range of about 1.0 to about 5.0 mm (about 0.04 toabout 0.20 in) and H_(br) within the range of about 30 to about 45 mm(about 1.18 to about 1.17 in). In the embodiment depicted in FIG. 2,T_(br) is about 2.8 mm (about 0.11 in) and H_(br) is about 36.5 mm(about 1.43 in). The backing ring may be of any appropriate material(e.g., electrical grade steels, high carbon steels, or combinationsthereof) and appropriate configuration (discrete pieces of magneticmaterial in contact with adjacent pieces to form a ring or amultiplicity of layers formed into a ring) for the application. In thedepicted embodiment of the present invention a multiplicity of layers ofelectrical grade steel.

Magnets

The rotor of the present invention further comprises a multiplicity ofpermanent magnets 40 having a thickness, T_(magnet), and a height,H_(magnet), in contact with an inner axial surface 32 of the backingring 30 and molded over by the polymeric frame 20 and spaced apart bythe magnet spacers 24 of the polymeric frame 20. The magnets may be anyappropriate material such as ferrite magnets. Typically, T_(magnet) iswithin the range of about 5.0 to about 15.0 mm (about 0.20 to about 0.60in) and H_(magnet) within the range of about 30 to about 45 mm (about1.18 to about 1.77 in). In the embodiment depicted in FIG. 2, T_(magnet)is about 6.4 mm (about 0.25 in) and H_(magnet) is about 36.5 mm (about1.43 in).

Rotor Dimensions

The foregoing aspects of the rotor of present invention allow for thedesign and production of rotors that are able to operate in the clotheswashing machines having one or more desirable characteristics such asrelatively low cost, relatively short in axial length (especially inview of the ability to have a relatively large diameter), relativelylight weight, relatively strong/durable coupling with the drive shaft.More particularly, the present invention may be used to produce a for arotor to have one or more of the following characteristics:

T_(br) may be about equal to T_(sidewall) and H_(br) may be about equalto T_(magnet),

H_(magnet) may be at least about 50% of the H_(rotor),

H_(magnet) may be at least about 55% of the H_(rotor),

H_(coupler) may be no more than about 45% of H_(rotor),

H_(coupler) may be no more than about 40% of H_(rotor);

OD_(coupler) may be no more than about 20% of OD_(rotor);

OD_(coupler) may be no more than about 15% of OD_(rotor);

OD_(hub) may be less than about 30% of OD_(rotor);

OD_(hub) may be less than about 20% of OD_(rotor);

T_(base) and T_(sidewall) may each be less than T_(magnet); and

T_(base) and T_(sidewall) may each be about less than 70% of T_(magnet).

EXAMPLE

A rotor in accordance with that depicted in FIGS. 1 and 2 and describedin detail above was tested by applying about 40 N-m of torque via ashaft onto which the rotor is installed. In comparison, a rotor with ametallic coupler essentially identical to that of the depictedembodiment except for instead of having other teeth, the metalliccoupler has an outer surface that is octagonal. The rotor depicted inthe figures having the toothed metallic coupler withstood theapplication of torque with no visible damage. In contrast, the rotorwith octagonal insert was damaged at the interface between the couplerand the hub and the octagonal insert began to rotate within the hub.Finite element analysis of the two rotors showed that plastic hub of therotor with the octagonal insert saw a maximum stress of about 47.75 MPawhereas the hub of the rotor with the splined metallic insert saw amaximum stress of about 7.25 MPa. Thus, utilizing the splined metallicinsert reduced the stress to the plastic hub by about 85%.

As various modifications could be made in the constructions and methodsherein described and illustrated without departing from the scope of theinvention, it is intended that all matter contained in the foregoingdescription or shown in the accompanying drawings shall be interpretedas illustrative rather than limiting. Thus, the breadth and scope of thepresent invention should not be limited by the above-described exemplaryembodiment, but should be defined only in accordance with the followingclaims appended hereto and their equivalents.

It should also be understood that when introducing elements of thepresent invention in the claims or in the above description of exemplaryembodiments of the invention, the terms “comprising,” “including,” and“having” are intended to be open-ended and mean that there may beadditional elements other than the listed elements. Additionally, theterm “portion” should be construed as meaning some or all of the item orelement that it qualifies. Moreover, use of identifiers such as first,second, and third should not be construed in a manner imposing anyrelative position or time sequence between limitations.

1. A rotor for an outer rotor-type electric motor, the rotor comprising:a metallic coupler that comprises: an inner axial surface configured tointerface with a shaft to be driven by the rotor when the motor isenergized; and an outer axial surface that corresponds to a multiplicityof outer teeth; a polymeric frame that comprises: a hub molded over atleast the outer axial surface of the metal coupler; a base that isintegrally formed with the hub and extending radially outward therefrom;a side wall that is integrally formed with the base; and a multiplicityof magnet spacers each of which is integrally formed with the side wall;a backing ring of a magnetic material molded over by the polymeric frameand having an outer axial surface in contact with the sidewall of thepolymeric frame; and a multiplicity of permanent magnets in contact withan inner axial surface of the backing ring and molded over by thepolymeric frame and spaced apart by the magnet spacers of the polymericframe.
 2. The rotor of claim 1, wherein the outer teeth are selectedfrom the group consisting of knurls, splines, keys, diamond knurls, orcombinations thereof.
 3. The rotor of claim 1, wherein the outer teethare knurls.
 4. The rotor of claim 1, wherein the number of outer teethis at least
 10. 5. The rotor of claim 1, wherein the number of outerteeth is at least 20 and no more than about
 40. 6. The rotor of claim 1,wherein the inner axial surface of the metal coupler corresponds to amultiplicity of inner teeth.
 7. The rotor of claim 6, wherein the innerteeth are selected from the group consisting of knurls, splines, keys,or combinations thereof.
 8. The rotor of claim 6, wherein the innerteeth are splines.
 9. The rotor of claim 1, wherein the metallic couplerfurther comprises one or more annular shoulders radially inward of, andaxially outward of each axial end of the outer axial surface and whereinthe hub is additionally molded over at least one of said annularshoulders such that it is generally flush with an axially outermostexterior surface of the metallic coupler.
 10. The rotor of claim 1,wherein the rotor has a height, H_(rotor), the permanent magnets have aheight, H_(magnet), that is at least about 50% of the H_(rotor).
 11. Therotor of claim 10, wherein H_(magnet) is at least about 55% of theH_(rotor).
 12. The rotor of claim 10, wherein the metal coupler has aheight, H_(coupler), that it is no more than about 45% of H_(rotor). 13.The rotor of claim 12, wherein H_(coupler) is no more than about 40% ofH_(rotor).
 14. The rotor of claim 12, wherein the rotor has an outerdiameter, OD_(rotor), and the metal coupler has a nominal outerdiameter, OD_(coupler), that is less than about 20% of OD_(rotor). 15.The rotor of claim 14, wherein OD_(coupler) that is less than about 15%of OD_(rotor).
 16. The rotor of claim 14, wherein the hub has an outerdiameter, OD_(hub), that is less than about 30% of OD_(rotor).
 17. Therotor of claim 16, wherein OD_(hub) is less than about 20% ofOD_(rotor).
 18. The rotor of claim 14, wherein the base has a thickness,T_(base), the sidewall has a thickness, T_(sidewall), the permanentmagnets have a thickness, T_(magnet), and wherein T_(base) andT_(sidewall) are each less than T_(magnet).
 19. The rotor of claim 18,wherein T_(base) and T_(sidewall) are each about less than 70% ofT_(magnet).
 20. The rotor of claim 18, wherein the backing ring has athickness, T_(br), that is about equal to T_(sidewall) and a height,H_(br), that is about equal to T_(magnet).
 21. The rotor of claim 1,wherein the polymeric frame further comprises a multiplicity ofreinforcement ribs each of which integrally formed with at least thebase.
 22. The rotor of claim 21, wherein each reinforcement rib has athickness, T_(rib), that is about equal to T_(base).
 23. The rotor ofclaim 21, wherein a number of the reinforcement ribs corresponding tothe number magnet spacers are each integrally formed with a magnetspacer and extend inward therefrom.
 24. The rotor of claim 23 whereineach of said spacer ribs extends to the hub and is also integrallyformed therewith.
 25. The rotor of claim 21, wherein one or more of thereinforcement ribs are concentric with the hub.
 26. The rotor of claim25, wherein a multiplicity of the reinforcement ribs extend from one ormore of said concentric ribs and are also integrally formed therewith.27. The rotor of claim 1, wherein the base of the polymeric framefurther comprises a multiplicity of openings.
 28. The rotor of claim 27,wherein the openings have a total surface area that is within a rangethat is from about 10% to about 30% of the nominal surface area of thebase.
 29. The rotor of claim 1, wherein the polymeric frame is formedfrom a filled or non-filled polymer, wherein the polymer is linear,branched, or crosslinked, and is selected from the group consisting ofpolyester, polyethylene, polypropylene, and copolymers thereof.
 30. Therotor of claim 29, wherein the polymer is polypropylene.
 31. The rotorof claim 1, wherein permanent magnets are ferrite magnets.
 32. The rotorof claim 1, wherein the backing ring is selected from the group ofelectrical grade steels, high carbon steels, or combinations thereof.33. The rotor of claim 1, wherein the backing ring is a comprises amultiplicity of layers of electrical grade steel.